Exhaust device comprising a cylinder head with a thermally decoupled integrated exhaust manifold

ABSTRACT

An exhaust device for a motor vehicle multi-cylinder internal combustion engine including a cylinder head of the engine in which there are exhaust ducts, a first end of each of which is connected to a combustion chamber of the engine and a second end of which opens into a cavity or plenum of an exhausted manifold integrated into the cylinder head of which an outlet duct is externally connected to a device for removing contamination from the exhaust gases of an exhaust line of the vehicle. The cavity or plenum of the manifold is formed in an element attached inside the cylinder head, and the element is thermally decoupled from the cylinder head using a thermal decoupling mechanism.

The invention relates to an exhaust device for a multicylinder internal combustion engine of a motor vehicle comprising a cylinder head of said engine in which are arranged exhaust ducts of which a first end of each is connected to a combustion chamber of said engine and of which the second end opens into a cavity or plenum of an exhaust manifold incorporated into the cylinder head of which an outlet duct is connected externally to a device for depolluting the exhaust gases of an exhaust line of the vehicle.

Many examples of devices of this type are known.

Conventionally, exhaust devices comprise exhaust ducts formed in the cylinder head of the engine which coincide with ducts of the manifold arranged facing the exhaust ducts. The manifold comprises at least one outlet duct which is connected to an exhaust line of the motor vehicle.

In order to reduce the content of pollutant products contained in the combustion gases, it is known practice to implant into the exhaust line depollution devices, notably catalyzers, which make it possible to convert the pollutant products present in the combustion gases, notably the unburnt hydrocarbons HC and the nitrogen oxides NOx.

A problem arises however when the engine is started up from cold.

Specifically, the effectiveness of the depollution devices is greatly dependent on their operating temperature. Having these devices at a distance from the combustion chambers of the engine slows down their rise in temperature during the first minutes of operation of the engine and reduces their effectiveness even though it is during these first minutes of operation of the engine that the largest quantity of pollutants is emitted.

To remedy this disadvantage, it has been proposed to produce exhaust manifolds that are partially or totally incorporated into the engine cylinder head, which makes it possible to considerably reduce the distance between the combustion chambers and the depollution device, which is then placed directly next to the cylinder head at the manifold outlet.

Document FR-2.738.289 describes notably a manifold of this type, wherein the exhaust ducts of the cylinder head open into a cavity or plenum half formed in the manifold and half in the cylinder head.

Document DE-A-3.815.408 describes, for its part, a manifold formed totally in the cylinder head and cast in one piece with the latter.

These known manifolds of the prior art however pose many problems.

Specifically, when a manifold of this type is only partly formed in the cylinder head, the distance between the combustion chambers and the depollution device is not reduced to the minimum and therefore the effectiveness of the depollution device is not total.

Furthermore, when the manifold is incorporated into the cylinder head, it is subjected to high temperature stresses and is therefore, like the material of the cylinder head, subjected to a considerable expansion as it rises in temperature. Therefore, it is practically impossible to couple such a manifold to the rest of the exhaust line if it is not provided with cooling cavities connected to the cavities for the circulation of liquid for cooling the cylinder head.

This design then reduces on the one hand from the efficiency of the engine since it is synonymous with reducing the thermal efficiency of the engine due to the need to cool the manifold, and, on the other hand, considerably reduces the benefits of having the manifold and the combustion chambers close together, the cooling of the manifold then no longer allowing its rapid rise in temperature to improve the effectiveness of the depollution device.

To remedy this disadvantage, the invention proposes a device of the type described above comprising a manifold incorporated into the cylinder head of the engine and furnished with means for thermally decoupling it from said cylinder head.

For this purpose, the invention proposes a manifold of the type described above, characterized in that the cavity or plenum of the manifold is formed in an element fitted to the inside of the cylinder head and in that said element is thermally decoupled from the cylinder head by thermal decoupling means.

According to other features of the invention:

-   -   the second ends of the exhaust ducts open into a receiving bore         formed in the cylinder head which receives a tubular insert         which is fitted to the inside of the cylinder head in order to         form the fitted element, which comprises orifices for         communication with the second ends of the exhaust ducts, and         which comprises the outlet duct opening to the outside of the         cylinder head,     -   the tubular insert is made of stainless steel,     -   the tubular insert is mounted without clearance in the receiving         bore of the cylinder head,     -   the thermal decoupling means are arranged in the cylinder head         around the tubular insert and at least between two consecutive         exhaust ducts,     -   the thermal decoupling means comprise at least one cavity which         is formed in the material of the cylinder head around the         receiving bore and which opens into said bore,     -   the device comprises a cavity which is arranged around the         receiving bore between each pair of consecutive exhaust ducts,         and a cavity which is arranged around the receiving bore between         an end exhaust duct and an end outer face of the cylinder head,     -   each cavity is produced when the cylinder head is molded.

Other features and advantages of the invention will appear on reading the following detailed description, for the comprehension of which reference will be made to the appended drawing in which the single FIGURE is a schematic view of a cylinder head for an exhaust device according to the invention.

The single FIGURE shows a cylinder head 10 for an exhaust device made according to the invention.

In a known manner, exhaust ducts 12 are arranged in the cylinder head 10. A first end 14 of each duct 12 is connected to a combustion chamber 16 of the engine and the second end 18 of each duct 12 opens into a cavity 20 or plenum of an exhaust manifold 22 incorporated into the cylinder head 10. An outlet duct 24 of the manifold 22 is connected externally to a device (not shown) for depolluting the exhaust gases of an exhaust line (not shown) of the vehicle. The cylinder head 10 comprises, between each combustion chamber 16, cavities 30 for the circulation of a liquid for cooling the engine.

According to the invention, the cavity 20 or plenum of the manifold 22 is formed in an element 26 which is fitted to the inside of the cylinder head 10 and said element 26 is thermally decoupled from the cylinder head 10 by thermal decoupling means 28.

More particularly, the second ends 18 of the exhaust ducts 12 open into a receiving bore 32 which is formed in the cylinder head 10. This bore 32 receives a tubular insert 26 forming the fitted element 26 which is fitted to the inside of the cylinder head, which comprises orifices 34 for communication with the second ends 18 of the exhaust ducts 12, and which comprises the outlet duct 24 opening to the outside of the cylinder head 10.

In the embodiment, the tubular insert 26 is made of stainless steel, because this material has thermal expansion characteristics suitable for ensuring a satisfactory seal when it is connected to the depollution device, irrespective of its temperature. It should be noted that this characteristic does not limit the invention, and that any other material having similar characteristics could be used for the correct application of the invention.

In the preferred embodiment of the invention, the tubular insert 26 is mounted without clearance in the receiving bore 32 of the cylinder head 10. The tubular insert 26 is for example sleeve-fitted into the bore 32 with an adjustment of the tight type.

Advantageously, the thermal decoupling means 28 are arranged in the cylinder head around the tubular insert 26 and at least between two consecutive exhaust ducts 12.

More particularly, the thermal decoupling means 28 comprise at least one cavity 28 which is formed in the material of the cylinder head 10 around the receiving bore 32, and which opens into said bore 32. This cavity is filled with air and therefore allows a thermal decoupling of the insert 26 relative to the cylinder head, preventing the heat of the cylinder head 10 from communicating with the insert 26 by conduction.

Preferably, as illustrated in the single FIGURE, the device comprises a cavity 28 which is arranged around the receiving bore 32 between each pair of consecutive exhaust ducts 12, and a cavity 28 which is arranged around the receiving bore 32 between an end exhaust duct 12 and an end external face 36 of the cylinder head 10.

Any production method may be used for the correct production of the cavities 28. However, in the preferred embodiment of the invention, each cavity 28 is made when the cylinder head 10 is molded.

The invention therefore makes it possible to benefit from a device comprising a manifold 26 fitted into the cylinder head 10 as close as possible to the combustion chambers 12, which makes it possible to optimize the performance of a depollution device connected to its outlet duct 24 and which does not have the disadvantages of the incorporated manifolds known in the prior art because of its thermal decoupling with respect to the cylinder head 10. 

1-7. (canceled)
 8. An exhaust device for a multicylinder internal combustion engine of a motor vehicle comprising: a cylinder head of the engine in which are arranged exhaust ducts of which a first end of each is connected to a combustion chamber of the engine and a second end opens into a cavity or plenum of an exhaust manifold incorporated into the cylinder head of which an outlet duct is connected externally to a device for depolluting exhaust gases of an exhaust line of the vehicle, of a type in which a cavity or plenum of the manifold is formed in an element fitted to an inside of the cylinder head and the fitted element is thermally decoupled from the cylinder head by thermal decoupling means, wherein the second ends of the exhaust ducts open into a receiving bore formed in the cylinder head that receives a tubular insert fitted to the inside of the cylinder head to form the fitted element, which comprises orifices for communication with the second ends of the exhaust ducts, and which comprises the outlet duct opening to the outside of the cylinder head.
 9. The exhaust device as claimed in claim 8, wherein the tubular insert is made of stainless steel.
 10. The exhaust device as claimed in claim 8, wherein the tubular insert is mounted without clearance in the receiving bore of the cylinder head.
 11. The exhaust device as claimed in claim 10, wherein the thermal decoupling means are arranged in the cylinder head around the tubular insert and at least between two consecutive exhaust ducts.
 12. The exhaust device as claimed in claim 11, wherein the thermal decoupling means comprises at least one cavity formed in the material of the cylinder head around the receiving bore and that opens into the bore.
 13. The exhaust device as claimed in claim 12, further comprising a cavity arranged around the receiving bore between each pair of consecutive exhaust ducts, and a cavity arranged around the receiving bore between an end exhaust duct and an end outer face of the cylinder head.
 14. The exhaust device as claimed in claim 12, wherein each cavity is produced when the cylinder head is molded.
 15. The exhaust device as claimed in claim 9, wherein the tubular insert is mounted without clearance in the receiving bore of the cylinder head.
 16. The exhaust device as claimed in claim 15, wherein the thermal decoupling means are arranged in the cylinder head around the tubular insert and at least between two consecutive exhaust ducts.
 17. The exhaust device as claimed in claim 16, wherein the thermal decoupling means comprises at least one cavity formed in the material of the cylinder head around the receiving bore and that opens into the bore.
 18. The exhaust device as claimed in claim 17, further comprising a cavity arranged around the receiving bore between each pair of consecutive exhaust ducts, and a cavity arranged around the receiving bore between an end exhaust duct and an end outer face of the cylinder head.
 19. The exhaust device as claimed in claim 17, wherein each cavity is produced when the cylinder head is molded. 